Ship to Shore: Linking Science to Policy

A little urban harbor reveals big mysteries

When the City of Redondo Beach woke up on Tuesday morning March 8th, 2011 to find its harbor brimming with a million dead sardines, the questions on every person’s mind were: what happened and who can find out quickly? Luckily, the last question was the easiest to answer because Sea Grant-funded USC Professors, Dr. David Caron and Dr. Astrid Schnetzer, have been closely monitoring and studying King Harbor in Redondo Beach since 2005, the last time a large fish kill occurred in the harbor. By taking water samples by hand each week and more recently by relying on permanently installed sensor technology in the harbor, Drs. Caron and Schnetzer have learned that there are several toxic species of algae that regularly live in the harbor and that the population levels of these species can change rapidly over short time periods. Similar to other marinas and harbors along the Southern California coast, King Harbor is occasionally the site of algal blooms, although most blooms have not been accompanied by large fish kills.

Given its history of algal blooms, Redondo Beach residents were quick to assume that the 170 tons of dead sardines floating in their harbor on March 8th were the result of an algal bloom or domoic acid poisoning. Domoic acid is a neurotoxin produced by the algae Pseudo-nitzschia and is known to cause short-term memory loss, seizures, paralysis, respiratory failure, and even death in marine mammals. Humans can be impacted as well as they can be exposed to the neurotoxin by eating contaminated shellfish, which bioaccumulate (accumulate in the tissues of an organism over time) the neurotoxin while filter feeding on the bloom of algae.

Surprisingly, what Drs. Caron and Schnetzer revealed through their monitoring data was that there was low algal biomass and no domoic acid in the harbor at the time of the fish kill on March 8th. In fact, the monitoring data revealed that on Monday the 7th, a large volume of cold, low-oxygen water came into the coastal area and harbor (which already has slow circulation and low oxygen levels) and the huge school of fish died from anoxia, or lack of oxygen. Even four days later on Friday the 11th, monitoring data documented that the harbor remained anoxic.

The mystery of the sardine kill continued, however, when Drs. Caron and Schnetzer found through tissue analysis in their labs that the sardines did indeed have detectable levels of domoic acid in their system, although likely not enough to kill them. This finding was critical from a public health perspective, as the close-working relationship between the researchers and the Redondo Beach city managers allowed the city to quickly issue warnings to its residents, many of whom had begun to collect the fish to eat once hearing that a toxic algal bloom was not the main cause of death. Although there was no domoic acid in the harbor, satellite imagery revealed that there was a massive greenish-brown Pseudo-nitzschia bloom offshore from Santa Barbara down to the Mexican border at this time. Drs. Caron and Schnetzer hypothesize that in order to avoid the bloom and/or the large volume of low-oxygen water heading toward the coastline, the sardines may have been forced into the small area of the harbor. With the arrival of the low-oxygen volume of water into the harbor, the large school of trapped sardines quickly consumed all the remaining oxygen in the water. It is possible, although virtually no data exist on the effects of domoic acid on fish like it does for mammals, that the small amounts of domoic acid in the fish was there from feeding farther offshore and possibly could have contributed to the unusual behavior of so many fish congregating in the harbor. Despite the unknown effects of the domoic acid in the fish tissue, however, it is clear that the depleted oxygen levels alone were enough to kill the fish once they were in the harbor.

For the city of Redondo Beach, understanding the science and causes behind what is happening in its harbor is critical for preventing or mitigating any of these blooms. The continuous monitoring research of King Harbor by Drs. Caron and Schnetzer is aimed at understanding the complex algal community dynamics naturally occurring in the harbor, the main role that toxic species play in this community, the role these toxic species play in blooms, and whether these blooms are originating inside the harbor or being advected into the harbor from the surrounding coastal waters. The event on March 8, 2011 shows how complex the interaction between the coastal marine ecosystem and oceanography can be along the Southern California coast. In simple visual terms, the problem of 170 tons of dead sardines may have looked as though it was confined only to Redondo Beach Harbor. In reality, the research and monitoring conducted by Drs. Caron and Schnetzer and their students demonstrated more complex and mysterious interactions between the offshore and inshore environments, as well as between oceanographic processes and marine organisms.

The long-term monitoring and tight association between the USC lab and the City of Redondo Beach allow for quick, coordinated action and dispersal of accurate information in the event of a possible health threat like the March 8th fish kill. King Harbor is not unique in having to deal with harmful algal blooms or anoxia, and the research of Drs. Caron and Schnetzer has the potential to inform a broad audience of coastal managers on the nature of toxin forming species and the initiation, progression, and demise of harmful algal blooms. This kind of information is urgently needed, as rates of harmful algal blooms seem to be increasing along the coastline of areas like Southern California; and the public is increasingly aware of the adverse and often severe impacts these blooms can have on marine organisms as well as human health.